Synchronizing device for a planet gear

ABSTRACT

A synchronizing arrangement in a planetary gear has an axially movable ring gear which for various gearchange positions can be coupled to either of two coupling rings, situated on their respective sides of the planetary gear, via synchronizing rings which belong to these coupling rings, are capable of limited rotation relative to the ring gear and have external locking teeth to prevent gear engagement before synchronization is achieved. The ring gear is provided with two grooves which run round its inside and each accommodates a ring-shaped locking device for transferring axial force to the respective synchronizing ring at the time of gear engagement. The respective locking device is also situated in an external groove in the relating synchronizing ring and can be compressed in the radial direction.

TECHNICAL FIELD

The present relates to a synchronizing arrangement for a planetary gearused in gearchange operations.

STATE OF THE ART

A known practice in heavy-duty vehicles such as trucks is for asupplementary gearbox to be connected to the vehicle's main gearbox todouble the number of possible gear ratios. Such a supplementary gearboxusually incorporates a planetary gear to make it possible to changebetween a low gear range and a high gear range. Gear changing in theplanetary gear is used in the low gear range but not in the high gearrange. A known practice for facilitating changing between high and lowgear ranges is to provide such planetary gears with synchronisingarrangements.

From the power distribution point of view it has been found advantageousto use the ring gear of the planetary gear as a connecting sleeve whichcan be brought, by axial movement, into engagement with coupling ringson both sides of the planetary gear. However, achieving efficientmanoeuvring of the synchronising rings which cooperate with the couplingrings and are necessary for achieving synchronisation has been foundproblematical when moving the ring gear in different directions in caseswhere the overall length of the planetary gear is short.

A solution to this problem has been indicated in Swedish patentspecification SE 463 477 (and its counterparts U.S. Pat. No. 5,083,993and EP 0 423 863). According to that solution, the ring gear is providedinside with a number of locking elements in the form of balls which arespring-loaded in the radial direction and cooperate with speciallydesigned shoulders on the synchronising rings in order, upon axialmovement of the ring gear, to cause the synchronising ring concerned tomove axially towards its coupling ring. Each locking element rests in aradial recess in the ring gear, and the locking elements are held inplace in pairs in the ring gear by means of a spring which extends in acircumferential direction in the ring gear and is anchored between thelocking elements in the ring gear by means of an axial pin. Thissolution has been found to work well, but a disadvantage is that arelatively large number of locking elements are required, withconsequent need for machining of the ring gear. Assembly is alsodifficult in that it involves many locking elements, springs and pins.

OBJECT OF THE INVENTION

The object of the invention is to provide a simplified synchronisingarrangement while maintaining good function.

DESCRIPTION OF THE INVENTION

The object of the invention is achieved by means of a synchronizedarrangement.

Providing the ring gear with only two ring-shaped locking devices whichhold themselves in place in internal grooves in the ring gear simplifiesboth machining and assembly. The locking devices themselves are also ofsimple design. The locking devices being fitted directly in the ringgear also means that no extra space is required in the axial or radialdirection. This makes possible a compact design of planetary gear.

Further features and advantages of the invention are indicated by thedescription and patent claims set out below.

A synchronizing arrangement in a planetary gear has an axially movablering gear which for various gearchange positions can be coupled toeither of two coupling rings, situated on their respective sides of theplanetary gear, via synchronizing rings which belong to these couplingrings, are capable of limited rotation relative to the ring gear andhave external locking teeth to prevent gear engagement beforesynchronization is achieved. The ring gear is provided with two grooveswhich run round its inside and each accommodates a ring-shaped lockingdevice for transferring axial force to the respective synchronizing ringat the time of gear engagement. The respective locking device is alsosituated in an external groove in the relating synchronizing ring andcan be compressed in the radial direction.

DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts a longitudinal section through a planetary gear accordingto invention with low gear engaged,

FIG. 2 depicts a longitudinal section corresponding to FIG. 1 but withneutral position engaged,

FIG. 3 depicts a longitudinal section corresponding to FIG. 1 but withhigh gear engaged,

FIG. 4 depicts schematically the position of cooperating coupling teethwhen low gear is engaged, and

FIG. 5 depicts a radial partial section through the ring gear of theplanetary gear.

DESCRIPTION OF AN EMBODIMENT

A planetary gear according to invention as depicted in FIGS. 1-3 maywith advantage constitute a supplementary gearbox intended to beconnected to a main gearbox of a heavy-duty vehicle such as a truck orbus. For the sake of simplicity, the housing which accommodates theplanetary gear 1 has been omitted.

The planetary gear 1 is arranged between an input shaft 2 from the maingearbox and an output shaft 3 from the supplementary gearbox. A sunwheel 4 is mounted on, and for joint rotation with, the input shaft 2,e.g. by means of splines, and is provided with external teeth 5 whichengage with a number of surrounding planet wheels 6. These planet wheels6 are each supported by their respective pivot pins 7 in a planet wheelcarrier 8 which is integrated with the output shaft 3. The sun wheel 4engages, in this case via teeth, and rotates jointly with a couplingring 9 provided with external coupling teeth 10 and held in place in theaxial direction on the input shaft 2 by a support ring 11. The couplingring 9 has a conical friction surface 12 facing outwards and intended tocooperate with a corresponding conical friction surface 13 facinginwards of a synchronising ring 14.

The housing, not depicted in detail, of the planetary gear 1 includes areaction disc 15 with a central hole in which a coupling ring 16 isfitted for joint rotation with it and is also fixed in the axialdirection, e.g. by means of splines and locking devices to make itpossible to remove it. On the coupling ring 16 there are externalcoupling teeth 17 and a conical friction surface 18, facing outwards,for cooperation with a corresponding conical friction surface 19, facinginwards, on a synchronising ring 20. The two synchronising rings 14 and20 are of the same design but are fitted mirror-image fashion on theirrespective sides of the planet wheels 6.

The planet wheels 6 and the two synchronising rings 14 and 20 aresurrounded by and engage with a ring gear 22 which is provided withinternal teeth 21 and is fitted movably in the axial direction relativeto the planet wheel and the coupling rings. This movability isaccomplished by means of an undepicted coupling fork intended to engagein an external recess 23 in the ring gear 22.

The ring gear 22 is provided at its ends with internal coupling teeth 24and 25 which are intended to cooperate with coupling teeth 10 and 17respectively on the coupling rings 9 and 16. It is advantageous that thecoupling teeth 24,25 and the teeth 21 on the ring gear 22 be integratedwith one another, as in the embodiment here depicted. The ring gear 22is provided with two grooves 26,27 running round its inside, one at eachend, at the transition between the teeth 21 and the respective couplingteeth 24,25. An annular locking device 28 is clamped in each of thesegrooves 26,27. As indicated in more detail by FIG. 5, these lockingdevices 28 each take the form of an annular curved wire, advantageouslywith circular cross-section, which sits springingly in the groove andhas a predetermined gap 29 between its opposite ends. This gap 29 allowsa certain radial compression together of the locking devices 28, as willbe described below.

The two synchronising rings 14 and 20 are provided with external lockingteeth 30,31 which during synchronising processes do in a conventionalmanner lock the gearchange movement so as to achieve synchronousrotation between the ring gear 22 and the respective coupling rings9,16. The two synchronising rings 14,20 are each provided with grooves32,33 respectively running round their outsides and incorporatinghollows 34,35 respectively. The locking devices 28 are movable in thesegrooves and hollows. The axial movement of the locking devices 28relative to the synchronising rings 14,20 is limited by a number ofexternal stop devices distributed in the circumferential direction oneach synchronising ring. The synchronising rings 14,20 have axiallyouter stop devices 36,37 respectively and axially inner stop devices38,39 respectively, in the form of teeth which fit in between the teeth21.

The planetary gear 1 according to invention works as follows. During agearchange operation, the ring gear 22 may be moved in either directionfrom a neutral position depicted in FIG. 2 to effect the gear change. Inthe neutral position, the two locking devices 28 each rest in theirgrooves 26,27 in the ring gear 22 and are thus situated close to theouter stop devices 36,38 on the synchronising rings 14,20. When the ringgear 22 moves to the right in FIG. 2, during engagement of low gearaccording to FIG. 1, the right locking device 28 will move thesynchronising ring 20 to the right so that it presses against thecoupling ring 16. Continuing movement of the ring gear will cause thelocking device 28 to be compressed radially so that the gap 29 betweenits ends decreases. At the same time, the locking device 28 will bepressed down into the hollow 35, after which the coupling teeth 25 onthe ring gear 22 can, when synchronisation is achieved, be insertedbetween the coupling teeth 17 on the coupling ring 16. At the same time,the second synchronising ring 14 is subjected only to an axial movementof the corresponding locking device 28 in the groove 32. At this stage,contact with the inner stop devices 37 will cause the left lockingdevice 28 to keep the synchronising ring 14 out of engagement with thecoupling ring 9.

Engaging high gear by moving the ring gear 22 to the left to theposition depicted in FIG. 3 from the neutral position in FIG. 2 resultsin the corresponding process whereby the left locking device 28 forcesthe synchronising ring 14 to the left and is compressed radially. Thecompression of the locking elements 28 is facilitated by the presence oframp-shaped transitions between the grooves 26,27 and the radially innersurface of the teeth 21.

The stop devices 36-39, particularly the inner stop devices 37,39, alsocause the ring gear 22 and the synchronising rings 14,20 to lockmutually in the circumferential direction, with a certain play. Asindicated by FIG. 4, there is a certain mutual play in thecircumferential direction because the stop devices 36,39 are narrower inthe circumferential direction than the gaps between the teeth 21. Thisfacilitates synchronisation and gear engagement.

The twisting moment to which the two synchronising rings 14,20 aresubjected during a gearchange operation is in the same direction duringa certain direction of rotation of the input shaft 2, e.g. duringdriving forwards when the input shaft 2 has a specified direction ofrotation. During reversing, the direction of rotation of the input shaft2 will be reversed, resulting in the twisting moment acting upon thesynchronising rings 14,20 likewise changing direction. In the embodimentdepicted, the direction of rotation of the input shaft 2 has beenassumed to be unchanged and such that in FIG. 4 the coupling ring 9 andhence also the synchronising rings 14,20 and the ring gear 22 endeavourto move upwards in the drawing.

To facilitate synchronised gearchanging during both driving forwards andreversing, it is desirable that the shape of the locking teeth 30,31 onthe synchronising rings be appropriate to the purpose, i.e. their shapeshould be such that when synchronisation is achieved the synchronisingrings can rotate to a position which allows gear engagement throughcompleted axial movement of the ring gear 22. The shape concerned may beselected as necessary and desired.

The planetary gear 1 described above is advantageous from themanufacturing and assembly point of view in that the necessary machiningof component parts is simple and the number of component parts is small.The design is also such as to occupy little space in both axial andradial directions. The fact that the mutually cooperating frictionsurfaces can be situated at relatively great radial distances from theshafts 2,3 means that the twisting moment acting during thesynchronising process as a result of friction forces may reach highvalues. This in turn means that the axial extent of the frictionsurfaces can be limited, thereby contributing to compact construction ofthe planetary gear.

The planetary gear described may of course also be used in othercontexts than that described here. It is possible, for example, to useit with hydraulic automatic gearboxes where a multiplicity of planetarygears are coupled together.

The invention may also be used in the type of synchronising arrangementsin which a multiplicity of synchronising rings are arranged on bothsides of the planetary gear.

1. A synchronizing arrangement for a planetary gear, wherein theplanetary gear includes first and second axially spaced apart couplingrings on a common rotation axis; an axially moveable ring gear extendingaround the rotation axis and situated axially between the first andsecond coupling rings, the ring gear being axially moveable in oppositeaxial directions for selectively coupling to either the first or thesecond of the coupling rings for achieving various respective gearpositions; a first synchronizing ring between the ring gear and thefirst coupling ring and extending around the rotation axis, a secondsynchronizing ring between the ring gear and the second coupling ringand extending around the rotation axis, the synchronizing rings beingsupported with respect to the ring gear to be rotatable in a limitedmanner relative to the ring gear around the axis; the first and secondsynchronizing rings having first and second external locking teethrespectively lockable with the ring gear on axial movement toward therespective one of the first and second synchronizing rings to lock thegear ring axial movement and provide connection to the respective one ofthe first and second coupling rings before synchronous rotation of thering and the respective one of the coupling rings is achieved;respective cooperating friction surfaces between the first synchronizingring and the first coupling ring and between the second synchronizingring and the second coupling ring and the friction surfaces at therespective one of the first and second synchronizing rings being adaptedto be pressed into friction engagement as the ring gear is moved in thedirection toward the respective one of the first and second couplingrings; a first and second locking device radially inward of the ringgear respectively toward each end of the ring gear and positioned withrespect to the ring gear and the synchronizing rings for transferringaxial force from the ring gear to the respective one of the first andsecond synchronizing rings at which the ring gear is to be coupled withthe respective one of the first and second coupling rings; a respectivefirst and second groove around the radial inside of the ring gear andtoward each axial end of the ring gear; a respective third and fourthgroove in the radial outside of the first and second synchronizingrings, respectively; each of the third and fourth grooves in the firstand second synchronizing rings respectively has a respective one of afirst and second hollow extending around the synchronizing ring andlocated toward the axial side of the grooves nearest to the respectivecoupling ring, the hollows being and positioned and shaped for receivingthe respective one of the first and second locking devices therein andalso being shaped for the locking devices to be compressed in thehollows by the ring gear being disposed to apply radial force to therespective locking device, and the ring gear being shaped for applyingsuch radial force as the ring gear is being moved toward the respectiveone of the first and second coupling rings where the locking device isin the respective hollow; each locking device comprising a substantiallyannular locking device which is capable of being compressed in theradial direction, the first locking devices being in each of the firstand third grooves and the second locking device being in the second andfourth grooves, enabling the locking device to move axially as the ringgear moves axially.
 2. The synchronizing arrangement of claim 1, furthercomprising radially outwardly protruding stops adjacent to and onopposite axial sides of the third and fourth grooves in thesynchronizing rings for limiting the mutual axial movement between thelocking device and the ring gear.
 3. The synchronizing arrangement ofclaim 1, further comprising radially outwardly protruding stops adjacentto and on opposite axial sides of the external third and fourth groovesin the synchronizing rings for limiting the mutual axial movementbetween the locking device and the ring gear.
 4. The synchronizingarrangement of claim 3, wherein the ring gear has teeth directedradially inwardly and at least the stop devices which are axially moreinward and toward each other are shaped and positioned to fit betweenthe teeth of the ring gear to lock the ring gear and the synchronizingrings mutually in the circumferential rotation direction.
 5. Thesynchronizing arrangement of claim 4, wherein the locking device is soshaped and the teeth of the ring gear are so shaped that each lockingdevice is compressed in the radial direction by the teeth on the ringgear when the ring gear is moved axially toward the respective one ofthe locking devices, as the ring gear moves axially to bring therespective synchronizing ring into engagement with the respectivecoupling ring.
 6. The synchronizing arrangement of claim 5, wherein eachof the third and fourth grooves in the first and second synchronizingrings respectively has a respective one of a first and second hollowextending around the synchronizing ring and located toward the axialside of the grooves nearest to the respective coupling ring, the hollowsbeing positioned and shaped for receiving the respective one of thefirst and second locking devices therein and also being shaped for thelocking devices to be compressed in the hollows by the ring gear beingdisposed to apply radial force to the respective locking device, and thering gear being shaped for applying such radial force as the ring gearis being moved toward the respective one of the first and secondcoupling rings where the locking device is in the respective hollow. 7.The synchronizing arrangement of claim 6, wherein the bottom of thehollow has a depth selected with respect to the teeth of the ring gearand the locking device has a thickness such that the thickness betweenthe teeth of the ring gear and the bottom of the hollow in each of thegrooves of the synchronizing rings is at least equal to the thickness ofthe locking device.
 8. A synchronizing arrangement for a planetary gear,wherein the planetary gear includes first and second axially spacedapart coupling rings on a common rotation axis; an axially moveable ringgear extending around the rotation axis and situated axially between thefirst and second coupling rings, the ring gear being axially moveable inopposite axial directions for selectively coupling to either the firstor the second of the coupling rings for achieving various respectivegear positions; a first synchronizing ring between the ring gear and thefirst coupling ring and extending around the rotation axis, a secondsynchronizing ring between the ring gear and the second coupling ringand extending around the rotation axis, the synchronizing rings beingsupported with respect to the ring gear to be rotatable in a limitedmanner relative to the ring gear around the axis; the first and secondsynchronizing rings having first and second external locking teethrespectively lockable with the ring gear on axial movement toward therespective one of the first and second synchronizing rings to lock thegear ring axial movement and provide connection to the respective one ofthe first and second coupling rings before synchronous rotation of thering and the respective one of the coupling rings is achieved;respective cooperating friction surfaces between the first synchronizingring and the first coupling ring and between the second synchronizingring and the second coupling ring and the friction surfaces at therespective one of the first and second synchronizing rings being adaptedto be pressed into friction engagement as the ring gear is moved in thedirection toward the respective one of the first and second couplingrings; a first and second locking device radially inward of the ringgear respectively toward each end of the ring gear and positioned withrespect to the ring gear and the synchronizing rings for transferringaxial force from the ring gear to the respective one of the first andsecond synchronizing rings at which the ring gear is to be coupled withthe respective one of the first and second coupling rings; a respectivefirst and second groove around the radial inside of the ring gear andtoward each axial end of the ring gear; a respective third and fourthgroove in the radial outside of the first and second synchronizingrings, respectively; each locking device comprising a substantiallyannular locking device which is capable of being compressed in theradial direction, the first locking devices being in each of the firstand third grooves and the second locking device being in the second andfourth grooves, enabling the locking device to move axially as the ringgear moves axially; each of the locking devices comprises a resilientring which is open with free ends and the resilient rings being shapedso that there is a gap between the free ends of the resilient rings,wherein the respective locking devices are fitted and positioned in thefirst and second grooves of the ring gear, each of the locking devicesbeing arranged so that when resting in the respective one of the firstand second grooves in the ring gear, the locking device is resilientlyfixed in the groove.